Optical modulators are used in a variety of systems. Controlled modulation of laser light is useful in analog systems to produce an output proportional to the input signal. Digital optical systems, such as fiber optic communication systems, use optical modulators to signal digital signals. In such case, a modulator is controlled to turn on and off. Digital optical modulators as signaling devices may also form the basis for optical memories and general computer devices. Possibilities for optical modulators in both digital and analog systems are increased with increased efficiency as measured with respect to the drive voltage required to produce the desired optical modulation.
Conventional modulators follow similar radio frequency transmission theory of attaining the desired transmission or reflection over the width of the pass band, typically attempting to use the center portion of the pass band or bands of the modulator. Conventional modulation of optical waves utilizes the change of the refractive index and/or the change of the absorption coefficient as a function of applied voltage to modulate the intensity or phase of an optical wave. Example conventional devices operating in this manner over their pass bands are the Mach-Zehnder modulator, the electro-optical phase modulator, the semiconductor electro-refraction modulator, and the electro-absorption modulator. Any of these modulators would be rendered more useful by an increased efficiency as a function of drive voltage.